Optical recording media on which information is accessed by means of a laser beam spot have conventionally been used widely as optical recording media which allow voice signals and image signals to be recorded and reproduced, In particular, magneto-optical disks on which information is recorded by means of heat from a laser beam spot,and a magnetic field from a magnet, phase-change optical disks on which information is recorded by means of phase changes caused by heat from a laser beam spot, etc. have been attracting attention as rewritable high-density recording media and research and development have been conducted intensively. Recently, amid strong demand for improvement in recording density of information recording media, technologies, such as magnetic super resolution (MSR) which limits a reproducible object to a smaller region than a laser spot by applying a reproducing magnetic field, have been sought to improve linear recording density greatly.
Such optical recording media are generally disk-shaped and have spiral or concentric tracks to record information. Each track is divided into plural sectors, each of which contains an ID region and data region. The ID region records ID data including a sector mark which indicates the start of the sector, address information which distinguishes the sector from other sectors, etc., while the data region records image data, voice data, document data, etc. Each optical recording medium is accessed on a sector-by-sector basis and the sector to be accessed is identified based on the ID data in the ID region.
Methods available to record and reproduce information in the data region include magneto-optical, phase-change, magnetic super resolution, and other recording methods. High recording densities have been achieved with research and development of recording methods.
However, all methods for recording ID data in ID regions use irregularities (emboss pits) in a substrate regardless of the type of recording medium and cannot read pits smaller in diameter than the beam. This reduces recording densities, making it necessary to provide a large area as the ID regions. Consequently, there is strong demand to improve the recording densities of the ID regions and reduce the area of the ID regions, thereby increasing total memory capacity of information recording media.